As air travel has increased over the past decades, airport facilities have become more crowded and congested. Minimizing the time between the arrival of an aircraft and its departure to maintain an airline's flight schedule, and also to make a gate or parking location available without delay to an incoming aircraft, has become a high priority in the management of airport ground operations. The safe and efficient ground movement of a large number of aircraft simultaneously into and out of ramp and gate areas has become increasingly important. As airline fuel costs and safety concerns and regulations have increased, the airline industry is beginning to acknowledge that continuing to use an aircraft's main engines, even at low thrust settings, to move aircraft during ground operations is no longer the best option. The delays, costs, and other challenges to timely and efficient aircraft pushback from airport terminals associated with the use of tugs and tow vehicles makes this type of aircraft ground movement an unattractive alternative to the use of an aircraft's main engines to move an aircraft on the ground. Restricted use of an aircraft's engines on low power during arrival at or departure from a gate is an additional, although problematic, option. Not only does such engine use consume fuel, it is also burns fuel inefficiently and produces engine exhaust that contains microparticles and other products of incomplete combustion. Operating aircraft engines, moreover, are noisy, and the associated safety hazards of jet blast and engine ingestion in congested gate and ramp areas are significant concerns that cannot be overlooked.
The use of landing gear motors and drive systems to drive aircraft autonomously during ground operations has been proposed by applicants and others, and a range of such motors and systems is described in the art. U.S. Pat. No. 7,469,858 to Edelson; U.S. Pat. No. 7,891,609 to Cox; U.S. Pat. No. 7,975,960 to Cox; and U.S. Pat. No. 8,109,463 to Cox et al., owned in common with the present invention, describe aircraft drive systems that use electric drive motors to power aircraft wheels and move an aircraft autonomously on the ground without reliance on aircraft main engines or external vehicles. U.S. Pat. No. 3,807,664 to Kelly et al. and U.S. Pat. No. 7,445,178 to McCoskey et al. describe aircraft wheel drive systems that use, respectively, hydraulic or electric motors to drive aircraft during taxi. U.S. Patent Application Publication Nos. US2009/0294577 to Rogues et al; US2010/0206980 to Cros et al.; US2011/0304292 to Charuel et al.; and U.S. Patent Application Publication No. US2012/0104158 to Charles et al. additionally describe various aircraft drive devices and motors controllable to move aircraft during ground operations. While the use of coupling elements or clutches is suggested in some of the foregoing aircraft wheel drive systems, it is not suggested that these coupling elements or clutches could be structured or function to automatically avoid engagement of the wheel drive system when the system should not be engaged, nor is it suggested that coupling element or clutch function could or should be enabled at defined drive modes, speeds, or other operating parameters.
U.S. Patent Application Publication No. US2010/0065678 to Kiyosawa describes a self-propelled wheel apparatus with a coaxially linked motor, wave gear, and a one-way clutch to drive an aircraft on the ground. The clutch in the Kiyosawa system, however, is stated to transmit rotational force to move the aircraft only in a reverse direction and to cause the wheel to rotate only when the aircraft moves backward. Such a clutch design could not function effectively to enable aircraft autonomous movement during all ground operations, including taxiing or movement in both forward and reverse directions, between landing and take off.
Automotive and like vehicle clutch assemblies that may be selectively engaged or disengaged are well known in the art. U.S. Pat. No. 3,075,623 to Lund; U.S. Pat. No. 3,599,767 to Soderquist; and U.S. Pat. No. 7,661,329 to Cali et al., for example, describe clutch assemblies incorporating sprag or pawl elements that may transmit torque between races or rotatable elements depending, in part, on their relative directions of rotation. One way vehicle clutches designed to lock in one direction and allow free rotation in the opposite direction are also available, as are improved selectable one way clutch designs, such as those described in U.S. Pat. No. 6,290,044 to Burgman et al.; U.S. Pat. No. 7,980,371 to Joki; and U.S. Pat. No. 8,042,670 to Bartos et al. Various other selectable clutch designs that provide controllable overrunning and coupling functions in automotive automatic transmissions, are described in U.S. Pat. No. 8,079,453 to Kimes and in U.S. Patent Application Publication Nos. US2010/0252384 to Eisengruber; US2011/0233026, US2013/0062151, and US2014/0102848 to Pawley; US2013/0277164 to Prout et al.; and US2014/0116832 to Beiser et al. While these clutch designs may function effectively in an automotive wheel environment, an aircraft landing gear drive wheel environment is significantly different and poses safety and other considerations that do not accompany the operation of automotive and like vehicles. Neither the foregoing clutch designs nor other commonly available clutch designs are sufficiently robust to function effectively and reliably in an aircraft landing gear drive wheel environment. It is not suggested that any of the foregoing clutch designs may be adapted to selectively and automatically transfer torque as required during operation of an aircraft electric taxi system in response to selected operating or other parameters. Nor is it suggested that these clutch designs are or could be adapted to avoid engagement of a drive system when it should not be engaged. Moreover, the clutches noted above do not provide the kind of failsafe capability that ensures that the clutch will never be engageable during flight, landing, takeoff, or during any other aircraft operating condition when operation of an electric taxi system would be unsafe.
A need exists for a clutch assembly adapted to function effectively and safely in an aircraft landing gear drive wheel drive system environment as an integral component of an aircraft electric taxi system. A additional need exists for a clutch assembly designed to automatically and selectively engage a drive motor to transfer torque and drive an aircraft drive wheel and move the aircraft autonomously on the ground only at predetermined speeds or operating conditions and/or in selected drive modes in a desired direction. A need also exists for a clutch assembly designed with a failsafe capability ensuring that the clutch assembly will never be engageable to activate the electric taxi system when aircraft operating conditions indicate that system operation is unsafe.